There is known a hologram recording technique of recording data to be recorded, as an interference pattern, into a hologram recording medium. In one method, light from a light source is spatially-modulated in accordance with the data to be recorded, by using a modulation pattern obtained by combining two-dimensional white and black patterns which are generated in accordance with a predetermined modulation rule, to thereby generate information light, and the recording medium is irradiated with the signal light and reference light The information light and the reference light form the interference pattern on the recording medium, and the interference pattern is recorded into a recording layer of the recording medium. On the other hand, in reproduction, the interference pattern recorded in the recording medium is irradiated with only the reference light, and detection light from the recording medium is detected by a two-dimensional (2D) sensor, to thereby reproduce the data
As in the information recording onto an optical disc or the like, even in the hologram recording, object light and the reference light are focused on the recording medium by using an objective lens or the like. Therefore, in order to accurately perform the information recording and reproduction, addressing control and tracking servo control are required, wherein the addressing control is to preferably recognize a position on the hologram recording medium and the tracking servo control is to control the position of the objective lens with respect to the hologram recording medium. In order to perform the addressing control and the tracking servo control, it is possible to use the hologram recording medium provided with: a hologram recording layer to record therein data; and an address information layer to record therein an address or the like (refer to patent documents 1 and 2). With respect to such a hologram recording medium, it is possible to record the data into the hologram recording medium while preferably performing the addressing control and the tracking servo control or the like, for example, by recording the data into the hologram recording layer with blue laser light and by reading the address or the like recorded in the address information layer with red laser light.    Patent document 1: Japanese Patent Application Laid Open NO. 2005-196826    Patent document 2: Japanese Patent Application Laid Open NO. 2005-71528
As one of the features of such a hologram recording technology, multiplex-recording (or shift-multiplex-recording) can be listed. The multiplex-recording is a technology for recording the data at a high density on the hologram recording medium by forming one interference pattern, which is to record one data, and another interference pattern, which is to record another data, with them superimposed on the hologram recording medium. This is a recording method that is possible because the recording layer or recording film of the hologram recording medium uses, for example, photopolymer or the like which is photo-polymerizable resin (hereinafter collectively referred to as “photopolymer”). The photopolymer has such a characteristic that constituent molecules with different refractive indexes in the photopolymer are polymerized and diffused by the irradiation of light, resulting in hardening after a certain time. Thus, the data can be multiplex-recorded before the photopolymer hardens, and as a result, the data can be recorded at a high density on the hologram recording medium.
On the other hand, it is assumed, even in the hologram recording medium, that sequential recording is performed, as in an optical disc such as a DVD, in order to efficiently use its recording capacity. In performing the sequential recording, an operation of restarting the recording (i.e. write-once or additional recording operation) is frequently performed after the recording is once stopped. Therefore, in restarting the recording, depending on a time elapsed after the stop of the recording, it is avoided to multiplex-record the data in a recording boundary portion because the photopolymer hardens. However, the hardening of the photopolymer requires a certain amount of time, so that not multiplex-recording the data in the recording boundary portion all the time (i.e. non-multiplexed recording) raises a technical problem of reducing the recording capacity of the hologram recording medium.
With regard to the subject to be solved by the present invention, the above can be listed as one example. It is therefore an object of the present invention to provide a hologram recording medium, a hologram recording apparatus and method, which allow the data recording while effectively using the recording capacity, and a computer program which makes a computer as such a hologram recording apparatus.
(Hologram Recording Medium)
The above object of the present invention can be achieved by a hologram recording medium provided with: a record information area in which record information is recorded; and a time information area to record therein time information which indicates a time length in which the record information can be multiplex-recorded.
According to the hologram recording medium of the present invention, the record information including video information, audio information, information for PC or the like can be recorded into the record information area. More specifically, by modulating the record information in accordance with a modulation rule related to the hologram recording/reproduction, a modulation pattern is generated from the record information. The modulation pattern is used in spatial-modulating the laser light emitted from an optical pickup or the like. The spatial-modulated laser light (i.e. information light or signal light) interferences with reference light of the laser light emitted from the optical pickup. Thereby, an interference pattern is recorded into the hologram recording medium. By this, the record information can be recorded into the record information area.
In particular, the hologram recording medium in the present invention is provided with the time information area to record therein the time information which indicates the time length in which the record information can be multiplex-recorded. More specifically, it is provided with the time information area to record therein the time information which indicates the time length (e.g. a time range, a time upper limit, or the like) in which the interference pattern can be superimposed and recorded by multiplex-recording (or shift-multiplex-recording), which is one feature of the hologram recording technology. Here, the time information may be information which directly or indirectly indicates the time length in which the record information can be multiplex-recorded.
As described above, because the time information which indicates the time length in which the record information can be multiplex-recorded is recorded, if the additional recording operation, which is frequently performed in the sequential recording, is performed, the additional recording operation can be performed with the multiplex-recording of the record information, depending on the time length between the temporary stop of the recording of the record information and the restarting of the recording. Specifically, if the time length between the temporary stop of the recording of the record information and the restarting of the recording is shorter than the time length indicated by the time information, the multiplex-recording of the record information can be performed in a additional recording boundary portion at which the additional recording operation is started. On the other hand, if the time length between the temporary stop of the recording of the record information and the restarting of the recording is longer than the time length indicated by the time information, the non-multiplex-recording of the record information can be performed (i.e. the record information cannot be multiplex-recorded) in the additional recording boundary portion at which the additional recording operation is started. By this, it is not necessary to always perform the non-multiplex-recording of the record information in the additional recording boundary portion, so that it is possible to record the record information while effectively using the recording capacity of the hologram recording medium.
In one aspect of the hologram recording medium of the present invention, the time information indicates a hardening time required to harden a material that constitutes the hologram recording medium after irradiation of a light beam, as the time length in which the record information can be multiplex-recorded.
According to this aspect, if the time length between the temporary stop of the recording of the record information and the restarting of the recording is shorter than the hardening time indicated by the time information, the multiplex-recording of the record information can be performed in the additional recording boundary portion at which the additional recording operation is started. On the other hand, if the time length between the temporary stop of the recording of the record information and the restarting of the recording is longer than the hardening time indicated by the time information, the non-multiplex-recording of the record information can be performed in the additional recording boundary portion at which the additional recording operation is started. The reason why the multiplex-recording can be performed on the hologram recording medium is that a recording layer or recording film of the hologram recording medium uses photopolymer or the like which is photo-polymerizable resin and which has a characteristic of hardening after a certain time from the irradiation of light. Therefore, with referent to the hardening time indicated by the time information, it can be judged relatively easily whether or not the photopolymer or the like has already hardened between the temporary stop of the recording of the record information and the restarting of the recording. By this, it is not necessary to always perform the non-multiplex-recording of the record information in the additional recording boundary portion, so that it is possible to record the record information while effectively using the recording capacity of the hologram recording medium. Incidentally, the recording layer or recording film of the hologram recording medium is not limited to the photopolymer or the like which is photo-polymerizable resin and which has a characteristic of hardening after a certain time from the irradiation of light. It is obvious that various materials that allow the hologram recording can be used.
Moreover, the hardening time indicated by the time information may be information which directly indicates the hardening time required to harden the material that constitutes the hologram recording medium (in particular, its recording layer or recording film) after the irradiation of the light beam. The hardening time indicated by the time information may be information which indirectly indicates the hardening time required to harden the material that constitutes the hologram recording medium (in particular, its recording layer or recording film) after the irradiation of the light beam
(Hologram Recording Apparatus)
The above object of the present invention can be also achieved by a hologram recording apparatus provided with: a recording device for recording record information into a hologram recording medium; a measuring device for measuring a time elapsed from the interruption of the recording of the record information to the restart of the recording of the record information; a first controlling device for controlling the recording device to restart the recording of the record information while the record information is multiplex-recorded, if the measured elapsed time is shorter than a time length in which the record information can be multiplex-recorded; and a second controlling device for controlling the recording device to restart the recording of the record information while the record information is not multiplex-recorded, if the measured elapsed time is longer than the time length in which the record information can be multiplex-recorded.
According to the hologram recording apparatus of the present invention, by the operation of the recording device, the record information including video information, audio information, information for PC, or the like can be recorded into the hologram recording layer on the hologram recording medium. More specifically, by modulating the record information in accordance with a modulation rule related to the hologram recording/reproduction, a modulation pattern is generated from the record information. The modulation pattern is used in spatial-modulating the laser light emitted from an optical pickup or the like, which constitutes one specific example of the first recording device. The spatial-modulated laser light (i.e. information light or signal light) interferences with reference light of the laser light emitted from the optical pickup. Thereby, an interference pattern is recorded into the hologram recording medium. By this, the record information can be recorded into the hologram recording medium.
In particular, in the present invention, by the operation of the measuring device, the elapsed time between the temporary stop of the recording of the record information and the restarting of the recording (in other words, the elapsed time between the temporary stop of the recording of the record information and the start of the additional recording operation) is measured. After that, if the measured elapsed time is shorter than the time length in which the record information can be multiplex-recorded, the recording device is controlled by the operation of the first controlling device to perform the multiplex-recording of the record information in the additional recording boundary portion at which the additional recording operation is started. On the other hand, if the measured elapsed time is longer than the time length in which the record information can be multiplex-recorded, the recording device is controlled by the operation of the second controlling device to perform the non-multiplex-recording of the record information in the additional recording boundary portion at which the additional recording operation is started. By this, it is not necessary to always perform the non-multiplex-recording of the record information in the additional recording boundary portion, depending on the time length between the temporary stop of the recording of the record information and the restarting of the recording. Thus, it is possible to record the record information while effectively using the recording capacity of the hologram recording medium. In particular, when the sequential recording is performed, it is predicted that the additional recording operation is frequently performed. Thus, according to the hologram recording apparatus of the present invention, it is possible to record the data while extremely effectively using the recording capacity of the hologram recording medium even if the sequential recording is performed.
In one aspect of the hologram recording apparatus of the present invention, the time length in which the record information can be multiplex-recorded is a hardening time required to harden a material that constitutes the hologram recording medium after irradiation of a light beam.
According to this aspect, if the time length between the temporary stop of the recording of the record information and the restarting of the recording is shorter than the hardening time indicated by the time information, the multiplex-recording of the record information can be performed in the additional recording boundary portion at which the additional recording operation is started. On the other hand, if the time length between the temporary stop of the recording of the record information and the restarting of the recording is longer than the hardening time indicated by the time information, the non-multiplex-recording of the record information can be performed in the additional recording boundary portion at which the additional recording operation is started. By this, it is not necessary to always perform the non-multiplex-recording of the record information in the additional recording boundary portion, so that it is possible to record the record information while effectively using the recording capacity of the hologram recording medium.
In another aspect of the hologram recording apparatus of the present invention, the first controlling device controls the recording device to record the record information from a position shifted by a first offset amount from a position of a record mark formed by recording the record information before the stop.
According to this aspect, by the operation of the first controlling device, it is possible to record the record information such that the record mark after the restarting of the recording is formed at the position shifted by the predetermined first offset amount from the position of the record mark formed by recording the record information before the stop. By this, it is possible to preferably perform the multiplex-recording of the record information.
In an aspect of the hologram recording apparatus in which the record information is recorded from the position shifted by the first offset amount, as described above, the first offset amount may be a shift amount in the multiplex-recording.
By virtue of such construction, it is possible to preferably perform the multiplex-recording of the record information, by the operation of the first controlling device.
In another aspect of the hologram recording apparatus of the present invention, the second controlling device controls the recording device to record the record information from a position shifted by a second offset amount from a position of a record mark formed by recording the record information before the stop.
According to this aspect, by the operation of the second controlling device, it is possible to record the record information such that the record mark after the restarting of the recording is formed at the position shifted by the predetermined second offset amount, which is different from the aforementioned first offset amount, from the position of the record mark formed by recording the record information before the stop. By this, it is possible to preferably perform the non-multiplex-recording of the record information.
In an aspect of the hologram recording apparatus in which the record information is recorded from the position shifted by the second offset amount, as described above, the second offset amount may be greater than or equal to a size of a diameter of the record mark.
By virtue of such construction, it is possible to preferably perform the non-multiplex-recording of the record information, by the operation of the second controlling device.
In an aspect of the hologram recording apparatus in which the record information is recorded from the position shifted by the second offset amount, as described above, the second offset amount may have an extent that is required to make the record mark formed by recording the record information before the stop not overlap the record mark of the record information recorded after the restarting of the recording.
By virtue of such construction, it is possible to preferably perform the non-multiplex-recording of the record information, by the operation of the second controlling device.
In another aspect of the hologram recording apparatus of the present invention, it is further provided with a storing device for storing time information which indicates the time length in which the record information can be multiplex-recorded.
According to this aspect, it is possible to preferably perform the aforementioned operations with reference to the time information stored in the storing device.
In another aspect of the hologram recording apparatus of the present invention, time information is recorded on the hologram recording medium, the time information indicating the time length in which the record information can be multiplex-recorded.
According to this aspect, it is possible to preferably perform the aforementioned operations with reference to the time information recorded on the hologram recording medium.
In another aspect of the hologram recording apparatus of the present invention, it is further provided with a third controlling device for controlling a recording power which is used when the recording device multiplex-records the record information, in accordance with the measured elapsed time, if the measured elapsed time is shorter than the time length in which the record information can be multiplex-recorded.
According to this aspect, by the operation of the third controlling device, the recording power (e.g. the value of the recording power) when the recording device multiplex-records the record information is controlled in accordance with how long the measured elapsed time is. More specifically explaining this, even if the elapsed time is shorter than the time length in which the multiplex-recording can be performed (in other words, the hardening time), the longer the elapsed time is, the more the photopolymer or the like that constitutes the hologram recording layer hardens. If the hardening of the photopolymer or the like progresses, recording features in recording the record information are different. Thus, with the same recording power, it is hard to maintain the good recording quality of the record information. Therefore, controlling the recording power by the operation of the third controlling device allows the good recording quality of the record information to be maintained.
Incidentally, when the non-multiplex-recording of the record information, the record information is recorded but not superimposed on the recording layer or recording film in which the hardening progresses due to the recording of the record information before the recording of the record information is restarted (i.e. before the recording of the record information is once stopped). Thus, it is not always necessary to consider the control of the recording power by the third controlling device. However, the recording power may be controlled even in the non-multiplex-recording of the record information.
In an aspect of the hologram recording apparatus provided with the third controlling device, as described above, the third controlling device may increase the recording power as the measured elapsed time is relatively long. That is, the third controlling device may increase the recording power more as the measured elapsed time becomes longer.
By virtue of such construction, it is possible to maintain the good recording quality of the record information. More specifically explaining this, if the hardening of the photopolymer or the like progresses, the sensitivity of the recording layer or recording film of the hologram recording medium decreases. Thus, in order to maintain the good recording quality of the record information that is recorded into the recording layer or recording film with the sensitivity reduced, it is necessary to relatively increase the recording power. Therefore, increasing the recording power by the operation of the third controlling device allows the good recording quality of the record information to be maintained.
Incidentally, the increasing amount of the recording power is preferably determined in accordance with the extent that the light beam or the like irradiated to newly record the record information overlaps the recording layer or recording film in which the hardening progresses due to the recording of the record information before the recording of the record information is restarted.
In an aspect of the hologram recording apparatus provided with the third controlling device, as described above, the third controlling device may increase the recording power, and then reduces the recording power step by step by a predetermined amount or continuously by a predetermined ratio.
By virtue of such construction, as the recording operation progresses, the record information is recorded but not superimposed on the recording layer or recording film in which the hardening progresses due to the recording of the record information before the recording of the record information is restarted. Thus, it is possible to reset the recording power to the original recording power by reducing the recording power gradually or step by step.
In another aspect of the hologram recording apparatus of the present invention, the recording device records the record information by irradiating a light beam, and the hologram recording apparatus further comprises a fourth controlling device for controlling an irradiation time of the light beam required to record the record information, in accordance with the measured elapsed time, if the measured elapsed time is shorter than the time length in which the record information can be multiplexed and recorded.
According to this aspect, it is possible to receive the same benefits as those in increasing the recording power by the operation of the aforementioned third controlling device. That is, increasing the recording power and increasing the irradiation time are common in the point of increasing the amount of energy given to the recording layer or recording film of the hologram recording medium. In the same manner, reducing the recording power and reducing the irradiation time are common in the point of reducing the amount of energy given to the recording layer or recording film of the hologram recording medium. Therefore, it is possible to maintain the good recording quality of the record information by controlling the irradiation time of the light beam (e.g. controlling a moving speed of an optical pickup) by the operation of the fourth controlling device, in addition to or instead of controlling the recording power by the operation of the third controlling device.
In an aspect of the hologram recording apparatus provided with the fourth controlling device, as described above, the fourth controlling device may increase the irradiation time as the measured elapsed time is relatively long.
By virtue of such construction, it is possible to maintain the good recording quality of the record information, as in increasing the recording power by the operation of the third controlling device.
In an aspect of the hologram recording apparatus provided with the fourth controlling device, as described above, the fourth controlling device may increase the irradiation time, and then reduces the irradiation time step by step by a predetermined amount or continuously by a predetermined ratio.
By virtue of such construction, it is possible to reset the irradiation time of the light beam to the original irradiation time, as in reducing the recording power gradually or step by step by the operation of the third controlling device. That is, it is possible to reset the extent of the energy given to the recording layer or recording film of the hologram recording medium, to the original extent.
(Hologram Recording Method)
The above object of the present invention can be also achieved by a hologram recording method in a hologram recording apparatus provided with: a recording device for recording record information into a hologram recording medium, the hologram recording method provided with a measuring process of measuring a time elapsed from the interruption of the recording of the record information to the restart of the recording of the record information; a first controlling process of controlling the recording device to restart the recording of the record information while the record information is multiplex-recorded, if the measured elapsed time is shorter than a time length in which the record information can be multiplex-recorded; and a second controlling process of controlling the recording device to restart the recording of the record information while the record information is not multiplex-recorded, if the measured elapsed time is longer than the time length in which the record information can be multiplex-recorded.
According to the hologram recording method of the present invention, it is possible to receive the same various benefits as those of the hologram recording apparatus of the present invention described above.
Incidentally, in response to various aspects as those of the hologram recording apparatus of the present invention, the hologram recording method of the present invention can also employ various aspects.
(Computer Program)
The above object of the present invention can be also achieved by a computer program for hologram recording control to control a computer provided in the aforementioned hologram recording apparatus of the present invention (including its various aspects), the computer program making the computer function as at least one portion of the measuring device, the first controlling device, and the second controlling device.
According to the computer program of the present invention, the aforementioned hologram recording apparatus of the present invention can be relatively easily realized as a computer reads and executes the computer program from a program storage device, such as a ROM, a CD-ROM, a DVD-ROM, and a hard disk, or as it executes the computer program after downloading the program through a communication device.
Incidentally, in response to the various aspects of the aforementioned hologram recording apparatus of the present invention, the computer program of the present invention can also employ various aspects.
The above object of the present invention can be also achieved by a computer program product in a computer-readable medium for tangibly embodying a program of instructions executable by a computer provided in the aforementioned hologram recording apparatus of the present invention (including its various aspects), the computer program product making the computer function as at least one portion of the measuring device, the first controlling device, and the second controlling device.
According to the computer program product of the present invention, the aforementioned hologram recording apparatus of the present invention can be embodied relatively readily, by loading the computer program product from a recording medium for storing the computer program product, such as a ROM (Read Only Memory), a CD-ROM (Compact Disc-Read Only Memory), a DVD-ROM (DVD Read Only Memory), a hard disk or the like, into the computer, or by downloading the computer program product, into the computer via a communication device. More specifically, the computer program product may include computer readable codes to cause the computer (or may comprise computer readable instructions for causing the computer) to function as the aforementioned hologram recording apparatus of the present invention.
These effects and other advantages of the present invention will become more apparent from the embodiments explained below.
As explained above, according to the hologram recording medium of the present invention, it is provided with the record information area and the time information area. According to the hologram recording apparatus, it is provided with the recording device, the measuring device, the first controlling device, and the second controlling device. According to the hologram recording method, it is provided with the measuring process, the first controlling process and the second controlling process. According to the computer program of the present invention, it makes a computer function as at least one portion of the measuring device, the first controlling device, and the second controlling device. Therefore, it is possible to record the record information while effectively using the recording capacity of the hologram recording medium.